This invention relates to a heat stabilized halogen-containing polymer composition normally susceptible to heat-induced deterioration which comprises a halogen-containing polymer and the degradation products of a latent mercaptan present during processing of the composition at an elevated temperature, said products being formed during said processing and including a liberated mercaptan. The free mercaptan enhances the activity of metal-based heat stabilizers such as organotin carboxylates and mercaptides in the polymer composition. It particularly relates to the stabilization against heat of vinyl chloride polymer compositions and articles made thereof by a latent mercaptan selected from the group consisting of 2-S-(hydroxyalkylthio) tetrahydropyran, 5-S-(hydroxyalkylthio) tetrahydrofuran, and the carboxylic acid esters thereof in combination with very low levels of a metal-based heat stabilizer or certain Lewis acids. Said latent mercaptans are also referred to hereinafter as 2-S-(tetrahydropyranyl)-thioalkanol, 2-S-(tetrahydropyranyl)thioalkyl carboxylate, and their furanyl homologs, i.e., 5-S-(tetrahydrofuranyl)-thioalkanol and 5-S-(tetrahydrofuranyl)thioalkyl carboxylate.
This invention also relates to articles of manufacture such as rigid pipe and window profile, flexible film, and semi-rigid tubing that are prepared from such heat-stabilized vinyl chloride polymer compositions.
It is well known that the physical properties of various organic polymers deteriorate and color changes take place during processing of the polymer and during exposure of formed polymer products to certain environments. Halogen-containing polymers are normally susceptible to heat-induced deterioration through autoxidation. The prime examples of such polymers are the vinyl and vinylidene polymers in which the halogen is attached directly to carbon atoms. Poly(vinyl chloride), copolymers of vinyl chloride and vinyl acetate, and poly(vinylidene chloride), the principal resin in self-clinging transparent food wraps, are the most familiar polymers which require stabilization for their survival during fabrication into pipe, window casings, siding, bottles, wall covering, packaging film, and the like. When such polymers are processed at elevated temperatures, undesirable color changes often occur within the first 5 to 10 minutes as well as during later stages of the processing. Haziness, which sometimes accompanies the color changes, is particularly undesirable where clear products are needed. The addition of heat stabilizers to such polymers has been absolutely essential to the wide-spread utility of the polymers. From a great deal of work in the development of more and more effective heat stabilizers there has emerged two principal classes: organotin compounds and mixed metal combinations. Organotin-based heat stabilizers are the most efficient and widely used stabilizers for rigid PVC. Synergistic combinations of alkyltin mercaptides and free mercaptans are particularly efficient heat stabilizers for rigid PVC during extrusion. They have not been entirely satisfactory, however, because of several failings on the part of the mercaptan synergist and are not used in flexible PVC. Many mercaptans give off an offensive odor even at room temperature and the odor grows worse at PVC processing temperatures. The oxidative stability of the mercaptans is very often very poor. Oxidation of the free mercaptans diminishes the synergism. A combination having an enhanced synergism would be welcomed especially by the flexible PVC industry. Also, because of the end-use of articles made from some polymers, many polymeric compositions require the presence of both biocides and heat stabilizers but the use of the organotin mercaptide/mercaptan combination in such a composition is often frustrated by the tendency of the free mercaptan to deactivate a biocide such as the much used OBPA (10, 10xe2x80x2-oxybisphenoxarsine).
Zinc salts in general have long been believed to be less satisfactory as heat stabilizers for halogen-containing polymers than the organotin-based stabilizers and, indeed, have lent their name to the catastrophic degradation known as zinc burn. In U.S. Pat. No. 3,660,331, Ludwig teaches the stabilization of vinyl halide resins by certain thioethers and thioesters of tetrahydropyran. Better heat stabilizer compositions are still needed, however. The thioether/low level metallic stabilizer combinations of this invention satisfy that need.
It has now been found that the activity of the 2-S-(tetrahydropyranyl)thioalkanol, the carboxylates thereof, and their furanyl homologs as heat stabilizers in halogen-containing polymer compositions is unexpectedly higher than that predicted on the basis of sulfur content when used in conjunction with very low levels of a metal-based stabilizer or a Lewis acid. Zinc salts are particularly valuable as synergists of latent mercaptans in their function as heat stabilizers for halogen-containing polymers. Zinc chloride, a Lewis acid, is of particular interest as such a synergist.
It is an object of this invention, therefore, to provide a heat stabilizer composition having the synergy of a mercaptan plus improved oxidative stability.
It is another object of this invention to provide a halogen-containing polymer composition stabilized against heat by 2-S-(tetrahydropyranyl)thioalkanols, carboxylates thereof, and their furanyl homologs in combination with a synergistic amount of a metal-based stabilizer or a Lewis acid.
It is another object of this invention to provide a PVC composition and article stabilized against heat by 2-S-(tetrahydropyranyl)thioalkanols, carboxylates thereof, and their furanyl homologs in combination with a synergistic amount of a metal-based stabilizer or a Lewis acid.
It is a related object of this invention to stabilize rigid, semi-rigid, and flexible PVC resin compositions with a heat stabilizer composition of this invention.
It is another object of this invention to provide a latent mercaptan-containing heat stabilizer composition which is substantially free from the offensive odor typically associated with mercaptans.
It is still another object of this invention to provide a flexible PVC composition and article stabilized against heat by a 2-S-(tetrahydropyranyl)thioalkyl carboxylate, its furanyl homolog, or a mixture thereof, in combination with a synergistic amount of a zinc salt.
These and other objects of the invention which will become apparent from the following description are achieved by adding a 2-S-(tetrahydropyranyl)thioalkanol, a carboxylate thereof, a furanyl homolog of either or both, or a mixture of two or more of said alkanols and esters, and a synergistic amount of a metal-based heat stabilizer or Lewis acid or a mixture of said metal-based heat stabilizer and Lewis acid to a halogen-containing polymer composition and processing the composition at an elevated temperature at which the latent mercaptan degrades to liberate a free mercaptan. The terms xe2x80x9clatent mercaptanxe2x80x9d and xe2x80x9cblocked mercaptanxe2x80x9d are used interchangeably herein.
Other products of the degradation of the blocked mercaptan are believed to include carbocations of the blocking moiety which are stabilized by a molecular structure in which the electron deficiency is shared by several groups. Resonance stabilization and neighboring group stabilization are two of the possible mechanisms by which the carbocations may be stabilized. The carbocations act as intermediates in the formation of stable compounds early in the hot processing of halogen-containing polymers. Although such mechanisms and the resultant carbocations are believed to be an impetus for the liberation of the active free mercaptan, this invention is in no way limited by the foregoing attempt to explain the working of the invention. Those skilled in the art will see the resonance stabilization and neighboring group stabilization that are possible in the following structures of the blocked mercaptan; other mechanisms may be at work in other blocked mercaptans represented by these structures that also liberate an active free mercaptan upon thermal and/or chemical degradation during processing of polymeric compositions containing such blocked mercaptans. For the purposes of this invention, the terms xe2x80x9cblocked mercaptanxe2x80x9d and xe2x80x9clatent mercaptanxe2x80x9d are used interchangeably to mean a thioether which degrades during processing of the composition at an elevated temperature to liberate a free mercaptan.
The term halogen-containing organic polymers as used herein means halogen-containing polymers or resins in which the halogen is attached directly to the carbon atoms. The halogen-containing polymers which can be stabilized according to this invention include chlorinated polyethylene having 14 to 75%, e.g. 27%, chlorine by weight, chlorinated natural and synthetic rubber, rubber hydrochloride, chlorinated polystyrene, chlorinated polyvinyl chloride, polyvinyl bromide, polyvinyl fluoride, and vinyl chloride polymers. The vinyl chloride polymers are made from monomers consisting of vinyl chloride alone or a mixture of monomers comprising, preferably, at least about 70% by weight of vinyl chloride, based on the total monomer weight. Examples of the copolymers include those made from vinyl chloride and from about 1 to about 30% of a copolymerizable ethylenically unsaturated material such as vinyl acetate, vinyl butyrate, vinyl benzoate, vinylidene chloride, diethyl fumarate, diethyl maleate, other alkyl fumarates and maleates, vinyl propionate, methyl acrylate, 2-ethylhexyl acrylate, butyl acrylate and other alkyl acrylates, methyl methacrylate, ethyl methacrylate, butyl methacrylate and other alkyl methacrylates, methyl alpha-chloroacrylate, styrene, trichloroethylene, vinyl ketones such as vinyl methyl ketone and vinyl phenyl ketone, 1-fluoro-2-chloroethylene, acrylonitrile, chloroacrylonitrile, allylidene diacetate, chloroallylidene diacetate, and vinyl ethers such as vinyl ethyl ether, vinyl chloroethyl ether, vinyl phenyl ether, and the vinyl ether prepared by the reaction of one mole of acrolein with one mole of ethylene glycol divinyl ether. Typical copolymers include vinyl chloride-vinyl acetate (96:4 sold commercially as VYNW), vinyl chloride-vinyl acetate (87:13), vinyl chloride-vinyl acetate-maleic anhydride (86:13:1), vinyl chloride-vinylidene chloride (95:5); vinyl chloride-diethyl fumarate (95:5), and vinyl chloride 2-ethylhexyl acrylate (80:20).
As used herein, the term PVC composition means a composition comprising a halogen-containing vinyl polymer in which the halogen is attached directly to a carbon atom. A rigid PVC composition is one which does not contain a plasticizer. A semi-rigid PVC composition is one which contains from 1 to about 25 parts of a plasticizer per 100 parts by weight of the halogen-containing vinyl polymer. A flexible PVC composition contains from about 25 to about 100 parts per 100 parts by weight of the halogen-containing vinyl polymer. Alkyl esters of carboxylic acids in which there are from 1 to 3 alkyl groups having from 8 to 12 carbon atoms are representative of the plasticizers. The alkyl group may be n-octyl, 2-ethylhexyl, nonyl, decyl, or dodecyl. Suitable esters include phthalates, trimellitates, benzoates, adipates, glutarates, and sebacates. The plasticizer may also be a pentaerythritol or such an ester thereof. A polymeric plasticizer is also suitable.
As used herein, a hydrocarbyl radical contains from 1 to 20 carbon atoms and may be an alkyl, cycloalkyl, aryl, arylene, alkaryl, aralkyl, or an aralkenyl or alkenyl radical having up to 3 ethylene double bonds; likewise, said radicals constitute the hydrocarbyl portion of a hydroxyhydrocarbyl radical. As used herein: a mono-valent radical has but one valence available for combining with another radical whereas a di-valent radical may combine with two other radicals; the term alkyl represents monovalent straight or branched chain hydrocarbon radicals; the term alkylenyl represents divalent, trivalent, and tetravalent straight or branched chain hydrocarbon radicals; the term oxyalkylenyl represents a divalent radical of a polyalkylene ether molecule having a polyalkoxy chain of from 2 to 4 of such radicals, wherein the alkylene moiety has 2 or 3 carbon atoms.
Also, as used herein: an acyloxyalkyl radical originates from a carboxylic acid ester of an alkyl alcohol; the R1 radical in Formula 1 below, therefore, in the stearic acid ester of mercaptopropanol is the stearoyloxypropyl radical; likewise, the R1 radical of the oleic acid ester of mercaptopropanol, which is one of the tallate esters of that alcohol, is the oleoyloxypropyl radical. The R1 radical of lauryl-3-mercaptopropionate, on the other hand, is dodecyloxycarbonylpropyl.
Substantially means largely if not wholly that which is specified but so close that the difference is insignificant.
The stabilizer compositions of this invention consist essentially of from about 87.5% to about 98.5%, preferably from about 93.5% to about 97.5%, by weight of a 2-S-(tetrahydropyranyl)thioalkanol, a 2-S-(tetrahydrofuranyl)thioalkanol, a carboxylate of either or both, or a mixture of two or more of said alkanols and esters, based on the total weight of the stabilizer composition, the balance comprising the metal-based stabilizer or Lewis acid. They are particularly suited to impart superior stabilization against the deteriorative effects of heat and ultra-violet light on both rigid and flexible PVC resins in comparison with stabilizer compositions previously known in the art. They may be prepared by blending the components thereof in any convenient manner which produces a homogeneous mixture, such as by shaking or stirring in a container. Likewise, the stabilizer compositions of this invention can be incorporated in a halogen-containing polymer by admixing the components of the stabilizer composition and of the polymer composition, such as, for example, in an appropriate mill or mixer or by any other of the well-known methods which provide uniform distribution of the stabilizer throughout the polymer composition.
One of the advantages of this invention is that the offensive odor of mercaptans is masked by a blocking group so that the latent mercaptan thus created may be put into a PVC composition or the like with little or no offense to the operator with the knowledge that the free mercaptan will be released as a degradation product when the treated composition is heated during the usual processing, e.g. extrusion.
The blocking compounds are preferably those which are capable of furnishing a stabilized carbocation having a molecular structure in which the electron deficiency is shared by several groups. Resonance stabilization and neighboring group stabilization are two of the possible mechanisms by which the carbocations may be stabilized.
The blocked mercaptans suitable for the purposes of this invention are represented by FORMULA 1: 
wherein a is 1, m is 0, n is 0 or 1; y is 1 or 2, and z is 1; R1 is a hydroxyalkyl group, a hydroxy(polyalkoxy)alkyl group, an acyloxyalkyl group, an acyloxy(hydroxyalkyl) group, acyloxy(alkoxyalkyl) group, an alkylene bis-(acyloxyalkyl) group, a hydroxy(polyalkoxy)acylalkyl group, an acyloxy(polyalkoxy)alkyl group, an oxy[bis(alkoxyacylalkyl)] group, an oxy[bis(polyalkoxyacylalkyl] group, a benzoyloxy(polyalkoxy)alkyl group, or a benzoyloxy(polyalkoxy)acylalkyl group, in which the alkyl moieties have from 2 to 20 carbon atoms, and the acyloxy moiety has from 2 to 22 carbon atoms; R2, R3, R4, and R5 are hydrogen; and either R3 or R5 is joined with R7 and O to form a heterocyclic moiety having 4 or 5 ring carbons with or without an alkoxy (C1-C4), aryloxy (C6-C10), alkaryloxy (C7-C14) or formyl substituent.
The mercaptans useful in this invention are the well-known mercaptoalkanols and mercaptocarboxylic acids and the esters of each. They include, but are not limited to, the following compounds: 
wherein R10 and R19 are independently OH, xe2x80x94O(Cxe2x95x90O)R17 xe2x80x94(Cxe2x95x90O)OR17, xe2x80x94SH, aryl, C1 to C18 alkyl, and xe2x80x94H;
R11 is xe2x80x94H, aryl, or C1 to C18 alkyl;
R17 is xe2x80x94H, alkyl, alkenyl, aryl, aralkyl, alkaryl, cycloalkyl, or cycloalkylenyl;
wherein i=0 or an integer from 1 to 6 inclusive.
Mercaptan-containing organic compounds preferred as intermediates in the preparation of the latent mercaptans of this invention are those compounds according to formula (MC1) where R11 is xe2x80x94H, R19 is xe2x80x94H, R10 is xe2x80x94O(Cxe2x95x90O)R7 or xe2x80x94(Cxe2x95x90O)OR17 and i=1; and those compounds according to formula (MC3) where R11 is xe2x80x94H and i=1.
Examples of mercaptan-containing compounds described by the above formulas include, but are not limited to, the following compounds: HSCH2CH2OH HSCH2CH2CH2OH HSCH2COOH HSCH2COOC8H17 HSCH2CH2CH2CH(OH)CH2CH(OH) HSCH2CH2OC(xe2x95x90O)C17H33 HSCH2CH2CH2OC(xe2x95x90O)C8H17 HSCH2CH2OC(xe2x95x90O)CHxe2x95x90CHC(Oxe2x95x90) OCH2CH2SH HSCH2CH2OC(xe2x95x90O)C11H23 HSCH2CH2OC(xe2x95x90O)CH2CH2C(xe2x95x90O)OCH2CH2SH HSCH2CH2OC(xe2x95x90O)(CH2)4C(xe2x95x90O)OCH2CH2SH 
[CH2CH2OC(xe2x95x90O)CH2]xe2x80x94C(OH)C(xe2x95x90O)OCH2CH2SH
In general, the procedure for making the latent mercaptans which are useful in this invention comprises adding the mercapto group of the free mercaptan across the double bonds of polarized, unsaturated compounds is as follows:
To a stirred mixture, under nitrogen atmosphere, of the mercaptan, acid catalyst, and optionally, a small percentage of antioxidant to inhibit radical reactions, is added dropwise to the polarized, unsaturated compound, either neat or in solution, while maintaining the temperature between 10xc2x0-70xc2x0 C. The mixture or solution is then heated for between 1 and 6 hours at 35xc2x0-70xc2x0 C. and conversion to product is monitored by gas chromatography and iodine titration for SH. The acid catalyst is removed by an alkaline wash and the resulting product is dried with magnesium sulfate and filtered. The solvent, if required, is removed under reduced pressure at  less than 50xc2x0 C. to yield the latent mercaptan. A solid phase catalyst may be used and then filtered out of the reaction mixture and regenerated for use in a subsequent synthesis, In this way, a wash step is eliminated.
The polarized, unsaturated compounds are exemplified by 3,4-dihydropyran; 3,4-dihydro-2-methoxy-2H-pyran; 3,4-dihydro-2-ethoxy-2H-pyran; 3,4-dihydro-2-phenoxy-2H-pyran; 3,4-dihydro-2-formyl-2H-pyran; and 2,3-dihydrofuran. The 3,4-dihydro-2-formyl-2H-pyran is made by the Diels-Alder dimerization of acrolein at high temperatures and pressures. The 3,4-dihydro-2-alkoxy-2H-pyrans and 3,4-dihydro-2-phenoxy-2H-pyran are made by the reaction of the corresponding vinyl ether with acrolein in the presence of a catalytic amount of a zinc salt, e.g., zinc chloride. A variety of 3,4-dihydro-2H-pyrans having a substituent in the 2-position can be made by similar reactions. The products formed by the reaction of 1 and 2 moles of acrolein with the divinyl ether of an alkylene- or polyalkylene glycol are blocking agents, also. The latent mercaptans made from the di-(3,4-dihydropyranyl) ethers also have the potential of being chelating agents in the polymer compositions of this invention. In the case of the reaction of one mole of acrolein per mole of a divinyl ether, the vinyl ether group of the resulting monomer permits the product to be incorporated into a vinyl chloride copolymer followed by the addition of a mercaptan across the double bond of the pyran ring to yield a latent mercaptan that is an integral stabilizer for the polymer. The reaction of one mole of acrolein with one mole of the divinyl ether also allows for the formation of a monomeric latent mercaptan of the mercaptan/tetrahydropyran adduct type in which the vinyl ether group of the resulting monomer permits the product to be copolymerized with one or more of a wide variety of ethylenically unsaturated compounds to form polymeric latent mercaptans. The product from the reaction of acrolein with chloroethyl vinyl ether provides a substituted 3,4-dihydropyran that can be further derivatized. The addition of a mercaptan across the double bond of the pyran ring can be done in the presence of the zinc salt catalyst to yield a stabilizer composition of this invention.
When 2-S-tetrahydopyranylthioethanol is prepared from 3,4-dihydropyran by said procedure, by-products having the following formulas (as each relates to FORMULA 1) are also obtained:
FORMULA
2. 
a=1, m=0, n=0, y=1, z=1; X is oxygen, R5 and R7 join to form xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94; R4 is hydrogen, and R1 is hydroxyethyl
3. 
a=1, m=0, n=1, y=1, z=1; X is oxygen, R3 and R7 join to form xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94; R2, R4 and R5 are hydrogen, and R1 is hydroxyethyl.
4. 
a=1, m=0, n=0, y=1, z=1; X is oxygen, R5 and R7 join to form xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94; R4 is hydrogen, and R1 is 2-ethoxytetrahydropyranyl.
5. 
a=1, m=0, n=0, y=1, z=1; X is oxygen, R5 and R7 join to form xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94; R4 is hydrogen, and R1 is 3-ethoxytetrahydropyranyl.
6. 
a=1, m=0, n=1, y=1, z=1; X is oxygen, R3 and R7 join to form xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94; R2, R4 and R5 are hydrogen, and R1 is 2-ethoxytetrahydropyranyl.
7. 
a=1, m=0, n=1, y=1, z=1; X is oxygen, R3 and R7 join to form xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94; R2, R4 and R5 are hydrogen, and R1 is 3-ethoxytetrahydropyranyl.
The homologous by-products are expected when 2,3-dihydrofuran is reacted with mercaptoethanol but the principal product is the 5-S-tetrahydrofuranylthioethanol shown by the following structure:
8. 
When the 3,4-dihydropyran is replaced by a 3,4-dihydro-2-alkoxy-pyran; a 3,4-dihydro-2-phenoxy-pyran; or a 3,4-dihydro-2-formyl-pyran in the above procedure, the following products are formed: 
Examples of 2-S-(tetrahydropyranyl)thioalkanols that are suitable as latent mercaptans for this invention include, without limitation, 2-S-(tetrahydropyranyl)thioethanol, 2-S-(tetrahydropyranyl)thiopropanol, and 2-S-(tetrahydropyranyl)-thiobutanol. The carboxylates suitable for the purposes of this invention are exemplified by 2-S-(tetrahydropyranyl)thioethyl caprate, which also may be named 2-S-(2-decanoyloxyethylthio) tetrahydropyran, made by the reaction between mercaptoethyl caprate and 3,4-dihydropyran according to the foregoing procedure and has the following formula in relation to FORMULA 1: 
wherein a=1, m=0, n=0; y=1, z is 1; X is oxygen, R5 and R7 are joined to form xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH24xe2x80x94; R is hydrogen, and R1 is decanoyloxyethyl.
Homologs of the thus described compounds which are particularly useful in the stabilization of flexible PVC compositions include the 2-S-(tetrahydropyranyl)thioalkyl carboxylates and their furanyl homologs wherein the ethyl moiety is replaced by propyl, butyl, hexyl, and others in the series up to and including dodecyl and the capric acid radical of said compound is replaced by other fatty acid radicals (saturated and unsaturated) or resin acid radicals having up to and including 22 carbon atoms. The acids are exemplified by caproic, caprylic, lauric, myristic, palmitic, stearic, arachidic, behenic, and the oleic and linoleic acids, as such, or as found in tall oil acids along with abietic and pimaric acids. The mercaptoalkyl carboxylate moiety is thus exemplified by mercaptoethyl laurate, mercaptoethyl oleate, mercaptoethyl hexanoate, mercaptoethyl octanoate, mercaptoethyl myristate, mercaptoethyl palmitate, mercaptoethyl stearate, and the mercaptopropyl, mercaptobutyl, and mercaptooctyl homologs of each of the above. The esters are made by the conventional method of reacting the hydroxyl group of a mercaptoalkanol with the desired carboxylic acid in the presence of an acidic catalyst and removing water as it forms.
The 2-S-(tetrahydropyranyl)thioalkanols, the carboxylates thereof, and their furanyl homolgs are employed in this invention in an amount sufficient to impart the desired resistance to heat deterioration to halogen-containing organic polymers. It will be readily apparent to one of ordinary skill in the art, that the precise amount of stabilizer composition used will depend upon several factors, including, but not limited to, the particular halogen-containing organic polymer employed, the temperature to which the polymer will be subjected, and the possible presence of other stabilizing compounds. In general, the more severe the conditions to which the halogen-containing organic polymer is subjected, and the longer the term required for resisting degradation, the greater will be the amount of stabilizer composition required. Generally, as little as about 0.20 part by weight of the latent mercaptan per hundred parts by weight of the PVC resin will be effective. While there is no critical upper limit to the amount of latent mercaptan which can be employed, amounts of about 3.0 parts or less by weight per hundred parts of the PVC resin are preferred.
A 2-S-(tetrahydropyranyl)mercaptoalkyl carboxylate is more active as a heat stabilizer in flexible PVC compositions than the tetrahydropyranyl-blocked mercaptans derived from alkylmercaptans such as dodecanethiol when activated according to this invention as manifest in the improved color hold properties and dynamic thermal stability of such stabilized PVC compositions. The higher activity may be the result of the better compatibility of the ester-containing latent mercaptans with a plasticized PVC. The compatibility of the corresponding homologous furan-based latent mercaptans is similar.
Metallic-based stabilizers are defined for the purposes of this invention as metal salt stabilizers, organometallic stabilizers. For the purposes of this invention, metal salts are defined to include oxides, hydroxides, sulfides, sulfates, chlorides, bromides, fluorides, iodides, phosphates, phenates, perchlorates, carboxylates, and carbonates. The metal salt stabilizers are exemplified by zinc, barium, strontium, calcium, tin, magnesium, cobalt, nickel, titanium, antimony, and aluminum salts of hydrochloric acid, sulfuric acid, phenols, aromatic carboxylic acids, fatty acids, epoxidized fatty acids, oxalic acid, acetic acid, and carbonic acid. Calcium stearate, calcium 2-ethylhexanoate, calcium octoate, calcium oleate, calcium ricinoleate, calcium myristate, calcium palmitate, calcium laurate, barium laurate, barium stearate, barium di(nonylphenolate), magnesium stearate, zinc octoate (or caprylate), zinc 2-ethylhexanoate, zinc stearate, zinc laurate, zinc oxide, zinc chloride, zinc hydroxide, zinc sulfide, zinc sulfate, zinc bromide, and Group I and II metal soaps in general are examples of suitable salts along with tin stearate, aluminum stearate, and hydrotalcite. The synergistic amount of the metallic-based stabilizer is from about 0.01 to less than 0.5%, preferably 0.02-0.4%, and more preferably 0.03-0.1% by weight of the halogen containing resin. The zinc salts are much preferred because they provide not only dynamic stability to the heat processed resin but also superior color hold properties in comparison with the other metal salts, especially at very low concentrations such as from 0.03 to 0.1%.
The Lewis acids are exemplified by boron trifluoride, aluminum chloride, zinc chloride and methyltin trichloride. Thus, there is some overlap between the metal salts and Lewis acids that are useful in this invention. The synergistic amounts of the Lewis acids for the purposes of this invention are from about 0.005 to less than 0.5%, preferably from about 0.01, more preferably from about 0.03, to about 0.1% by weight of the halogen-containing resin. The Lewis acids and the metallic-based stabilizers may be used in combination.
Conventional organometallic stabilizers include the organotin carboxylates and mercaptides. Such materials include butyltin tris dodecyl mercaptide, dibutyltin dilaurate, dibutyltin didodecyl mercaptide, dianhydride tris dibutylstannane diol, dihydrocarbontin salts of carboxy mercaptals such as those set forth in Hechenbleikner et al.(U.S. Pat. No. 3,078,290). There can be included any of the vinyl chloride resin stabilizers set forth in Salyer (U.S. Pat. No. 2,985,617).
Monosulfides and/or polysulfides of the organotin mercaptides of carboxylates and/or mercaptoalkyl carboxylates and of alkyl thioglycolates are also suitable as metal based stabilizers in the compositions of this invention for improving the resistance of halogen-containing polymers to deterioration when heated to 350xc2x0 F. (177xc2x0 C.) during processing. The sulfides may be made by heating stoichiometric quantities of a mercaptoalkyl ester of a carboxylic acid or an alkyl mercaptocarboxylate and an organotin chloride having the formula:
Rxe2x80x2(4xe2x88x92z)SnHalzxe2x80x83xe2x80x83II
wherein Rxe2x80x2 is an alkyl group having from 1 to 12 carbon atoms, Hal is a halogen having an atomic weight of from 35 to 127, preferably chlorine, and z is any number from 1 to 3;
in water and ammonium hydroxide to about 30xc2x0 C. (86xc2x0 F.), slowly adding an alkali metal mono- or polysulfide, and heating the reaction mixture further to about 45xc2x0 C. before separating the product from said mixture.
Alternatively, the sulfide may be made by mixing a monoalkyl- or dialkyltin sulfide with an organotin mercaptide and by other procedures well known in the stabilizer art.
The sulfides of a mercaptoalkyl ester of a carboxylic acid are characterized by an equilibrium mixture of one or more alkyltin halides of Formula II, one or more mercaptides of Formula III and one or more alkyltin mono- or polysulfides or oligomers thereof and the alkyltin mono- and polysulfides having the formula IV.
R*(4xe2x88x92n)xe2x80x94Snxe2x80x94[[Sxe2x80x94Zxe2x80x94[OC(xe2x95x90O)R1*]m]]nxe2x80x83xe2x80x83Formula III
wherein R* is an alkyl radical having from 1 to 12 carbon atoms; R1* is hydrogen, a hydrocarbyl radical, a hydroxyhydrocarbyl radical, or R2*C(xe2x95x90O)OR3*, wherein R2* is alkylene, hydroxyalkylene, phenylene, or xe2x80x94CH=CHxe2x80x94, and R3* is hydrogen, a hydrocarbyl radical, a hydroxyhydrocarbyl radical, or an alkylcarboxyalkylene radical; Z is an alkylene or hydroxyalkylene radical of at least 2 carbon atoms up to 20 carbon atoms; m is an integer from 1 to 3, n is from 2 to 3, and the valency of Z is m+1.
Formula IV is representative of linear structures as well as of cyclic trimers and adamantyl rings:
[R4*(4xe2x88x92x)SnS(p/2)]Mxe2x88x92[R5*(4xe2x88x92y)SnS(q/2)]Nxe2x80x83xe2x80x83Formula IV
wherein R4* and R5* are independently alkyl radicals having from 1 to 12 carbon atoms and are bonded to Sn; x is 2 or 3; y is 2 or 3; p and q are 2 to 20, preferably 2-4; and M and N are 0-10, preferably 0-4, but Mxe2x89xa0N=0; with the proviso that when (4xe2x88x92x)=(4xe2x88x92y), p=q, and when (4xe2x88x92x)xe2x89xa0(4xe2x88x92y), pxe2x89xa0q.
It should be understood that the structures of the sulfides produced by the processes mentioned above are very complex. The reactions are believed to produce an equilibrium mixture composed of several different but related products. As will be appreciated by those of ordinary skill in chemistry, equilibrium mixtures inherently include the starting materials as well as the products of any reaction between them. The chemical and patent literature contain numerous examples demonstrating that members of different classes of organotin compounds may react with one another under certain conditions to yield products containing one or more tin atoms wherein at least a portion of the tin atoms are bonded to different combinations of radicals than they were before being mixed together. Accordingly, the sulfides are believed to include bis[monoorganotin)-bis(thioalkyl carboxylate)] monosulfides and polysulfides, bis[(diorganotin)-mono(thioalkyl carboxylate)]monosulfides and polysulfides, and products which arise during equilibrium reactions among said mono- and polysulfides, including monoalkyltin tris(thioalkyl carboxylates), dialkyltin bis(thioalkyl carboxylates), mono- and di-organotin mono- and polysulfides, and oligomers thereof, as well as the starting materials themselves. The sulfide of an alkyl ester of a mercaptocarboxylic acid is likewise believed to include bis[monoorganotin)-bis(alkyl mercaptocarboxylate)] monosulfides and polysulfides, bis[(diorganotin)-mono(alkyl mercaptocarboxylate)]monosulfides and polysulfides, and products which arise during equilibrium reactions among said mono- and polysulfides, including monoalkyltin tris(alkyl mercaptocarboxylates), mono- and di-organotin mono- and polysulfides, and oligomers thereof.
The polysulfides include mixtures of compounds having from 2 to 10 sulfur atoms linked together. Mixtures of monosulfides and polysulfides having from 2 to 4 sulfur atoms are preferred.
Conventional non-metallic stabilizers and antioxidants can also be included in the PVC compositions of the present invention. Thus, there can be included 0.01-0.75%, based on the weight of the resin, of sulfur containing compounds such as dilauryl-thiodipropionate, distearyl 3,3xe2x80x2-thiodipropionate, dicyclohexyl-3,3-thiodipropionate, dioleyl-3,3xe2x80x2-thiodipropionate, dibenzyl-3,3xe2x80x2-thiodipropionate, didecyl-3,3xe2x80x2-thiodipropionate, dibenzyl-3,3xe2x80x2-thiodipropionate, diethyl-3,3xe2x80x2-thiopropionate, lauryl ester of 3-methylmercaptopropionic acid, lauryl ester of 3-butylmercaptopropionic acid, lauryl ester of 3-lauryl mercaptopropionic acid, and phenyl ester of 3-octyl mercaptopropionic acid.
In addition to the stabilizer compositions of this invention, the PVC compositions of this invention may contain plasticizers, as mentioned above in regard to flexible PVC, and conventional additives such as pigments, fillers, blowing agents, dyes, ultraviolet light absorbing agents, antioxidants, densifying agents, biocides, and the like.
An antioxidant may be added in an amount of 0.01-10%, preferably 0.1-5% by weight of the PVC resin. Phenolic antioxidants are particularly suitable and are exemplified by 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, propyl gallate, 4,4xe2x80x2-thiobis(6-t-butyl-m-cresol), 4,4xe2x80x2-cyclohexylidene diphenol, 2,5-di-t-amyl hydroquinone, 4,4xe2x80x2-butylidene bis(6-t-butyl-m-cresol), hydroquinone monobenzyl ether, 2,2xe2x80x2-methylene-bis(4-methyl-6-t-butyl phenol), 2,6-butyl-4-decyloxy phenol, 2-t-butyl-4-dodecyloxy phenol, 2-t-butyl-4-dodecyloxy phenol, 2-t-butyl-4-octadecyloxy phenol, 4,4xe2x80x2-methylene-bis(2,6-di-t-butyl phenol), p-amino phenol, N-lauryloxy-p-amino phenol, 4,4xe2x80x2-thiobis (3-methyl-6-t-butyl phenol), bis [o-(1,1,3,3-tetramethyl butyl)phenol] sulfide, 4xe2x88x92acetyl-xcex2-resorcylic acid, A-stage p-t-butylphenolformaldehyde resin, 4-dodecyloxy-2-hydroxybenzophenone, 3-hydroxy-4-(phenylcarbonyl) phenyl palmitate, n-dodecyl ester of 3-hydroxy-4-(phenyl carbonyl) phenoxyacetic acid, and t-butyl phenol.
From 0.01-30% by weight of an epoxy compound, based on the weight of the vinyl chloride polymer in the PVC compositions of this invention may also be used. Examples of such epoxy compounds include epoxidized soya bean oil, epoxidized lard oil, epoxidized olive oil, epoxidized linseed oil, epoxidized castor oil, epoxidized peanut oil, epoxidized corn oil, epoxidized tung oil, epoxidized cottonseed oil, epichlorhydrin/bis-phenol A resins, phenoxy-propylene oxide, butoxypropylene oxide, epoxidized neopentylene oleate, glycidyl epoxystearate, epoxidized xcex1-olefins, epoxidized glycidyl soyate, dicyclopentadiene dioxide, epoxidized butyl toluate, styrene oxide, dipentene dioxide, glycidol, vinyl cyclo-hexene dioxide, glycidyl ether of resorcinol, glycidol ether of hydroquinone, glycidyl ether of 1,5-dihyroxynaphthalene, epoxidized linseed oil fatty acids, allyl glycidyl ether, butyl glycidyl ether, cyclohexane oxide, 4-(2,3-epoxypropoxy) aceto-phenone, mesityl oxide epoxide, 2-ethyl-3-propyl glycidamide, glycidyl ethers of glycerine, pentaerythritol and sorbitol, and 3,4-epoxycyclohexane-1,1-dimethanol bis-9,10-epoxystearate.
Likewise there can be used organic phosphites in an amount of 0.01 to 10%, preferably 0.1-5% by weight of the vinyl chloride polymer. The organic phosphites contain one or more, up to a total of three, aryl, alkyl, aralkyl and alkaryl groups, in any combination. The term xe2x80x9ctrialkylarylxe2x80x9d is inclusive of alkyl, aryl, alkaryl and aralkyl phosphites containing any assortment of alkyl, aryl, alkaryl and aralkyl groups. Exemplary are triphenyl phosphite, tricresyl phosphite, tri(dimethylphenyl) phosphite, tributyl phosphite, trioctyl phosphite, tridodecyl phosphite, octyl diphenyl phosphite, dioctyl phenyl phosphite, phosphite, octyl diphenyl phosphite, dioctyl phenyl phosphite, tri(octyl-phenyl) phosphite, tri(nonylphenyl) phosphite, tribenzyl phosphite, butyl dicresyl phosphite, octyl di(octyl-phenyl) phosphite, tri(2-ethyl-hexyl) phosphite, tritolyl phosphite, tri(2-cyclohexylphenyl) phosphite, tri-alpha-naphthyl phosphite, tri(phenylphenyl) phosphite, and tri(2-phenylethyl) phosphite.
Likewise there can be included from 0.01-10% by weight of the vinyl chloride polymer of a polyol stabilizer for vinyl chloride resins. Thus there can be included glycerol, sorbitol, pentaerythritol, mannitol and polyethers such as diethylene glycol, triethylene glycol, tetraethylene glycol, tripropylene glycol, and the like.
Nitrogen containing stabilizers such as dicyandiamide, melamine, urea, formoguanamine, dimethyl hydantoin, guanidine, thiourea, 2-phenylindoles, aminocrotonates, N-substituted maleimides, uracil, the 1,3-dialkyl-6-amino-uracil derivatives described in German Offenlegungsschrift 19,741,778 by Ciba Specialty Chemicals Holding Inc., and the pyrrolodiazine diones described in published Australian Patent Application No. AU-A-48232/96 by Ciba-Geigy, and the like also can be included in amounts of 0.1-10% by weight. Of particular interest are the pyrrolodiazine diones described by the formula: 
wherein R{circle around (1)}, R{circle around (2)}, R{circle around (3)}, and R{circle around (4)} are independently hydrogen or C1-C4 alkyl. Examples of compounds contemplated for use in this invention include the 1H-pyrrolo[2,3-d]pyrimidine-2,4(3H,7H)-diones exemplified by Compound Nos. 103, 111, 123, 129, and 131 of said Australian Patent Application, which have the following substituents:
No. 103 1,3,6-trimethyl;
No. 111 1,3,6,7-tetramethyl;
No. 123 none;
No. 129 1,3-diethyl,6-methyl;
No. 131 1,3-di-n-butyl,6-methyl;
Said compounds may be prepared by the method described by S. Senda and K. Hirota, Chem. Pharm. Bull., 22(7), 1459-1467(1974) or by the reaction of the corresponding aminouracil with molar excesses of chloroacetaldehyde and ammonium acetate in water at about 65xc2x0 C. until a precipitate forms or with molar excesses of acetoxyacetone and ammonium acetate in water at reflux for 12 hours. The German Offenlegungsschrift 19,741,778 and the Australian Patent Application No. AU-A-48232/96 are each incorporated herein by reference.
Conventional lubricants for vinyl chloride resins such as low molecular weight polyethylene, i.e. polyethylene wax, fatty acid amides, e.g. lauramide and stearamide, bisamides, e.g. decamethylene, bis amide, and fatty acid esters, e.g. butyl stearate, glyceryl stearate, linseed oil, palm oil, decyloleate, corn oil, cottonseed oil, hydrogenated cottonseed oil, stearic acid, calcium stearate, mineral oil, montan wax, oxidized polyethylene and the like can also be included.